Dovecot fails to deliver to all mail clients

I am new to linux and recently created a mail server on a SusE linux 10.2 Machine using POstfix and Dovecot.

Postfix seems to be working fine as mail gets delivered to all user's mail boxes and on checking mail on thbe mboxes it is there. However I am unable to read mail using a client such Kmail, Mutt, Outlook, Outlook Express.

When I use Telnet on port 110 I am able to loging using user's login credentials, but on running the command 'stat' it shows that there is no mail. but mail is there cause I have checked manually and /var/log/dovecot.log shows the following.

No, you dont have to of course. But as you posted this in the forum of the ispconfig 3 software I asked for the version as not all versions support dovecot. I moved your post to the general linux admin forum now.